Sudden change in menstrual cycle?

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I've been on the same pill for maybe 2/2.5 years now? My periods are always the same. They come on the third day and last the entire duration. But now I'll get the cramps and the cravings, get my period the following morning along with cramps like usual, but I'll have a super light flow and it will be gone the next day? It's been like this for 2 maybe 3 months now. I've taken test after test and they come back negative. Anyone ever go through this or have any insight?